Feedback coupling circuit



I 1 9 8 GROSS REFEREE-ICE SEARCH ROOM Sept. 26, 1950 v A. G. KANDOlAN 2,523,307

FEEDBACK COUPLING CIRCUIT Filed 001:. 28, 1944 N a E/ m W Q l EL Q v N @277 J L N/ Q s INVENTOR. ARM/6 G. KANDO/fl/V ATTUIEWEY Patented Sept. 26, 1950 UNITED STATES PATENT OFFICE 2,523,3 7 I I FEEDBACK COUPLING CIRCUIT Armig G. Kandoian, New York, 'Y., assignor to Federal Telephone and Radio Corporation, New York, Y., a corporation of- Delaware Application '0ctober'28, 1944,- Serial No. 560,790

7 01m (01. ire-171) This invention relates to electron discharge device circuits and particularly to the feed-back of energy from the output circuit to the input circuit thereof.

In certain electron discharge device circuits, energy is fed back from the output circuit to the input circuit. In oscillators, positive feed-back is used to produce oscillations and in amplifiers, negative feed-back is used among other things to prevent oscillation and produce greater stability of operation.

An object of the present invention is the provision in an electron discharge device circuit of improved feed-back means enabling improved control of. the energy fed back.

Another object of the present invention is-the provision of such improved energy feed-back means in which the phase and amplitude of the energy fed back are separately controlled.

In most electron discharge device oscillators, a slight amount of feed-back is usually sufficient to sustain oscillations. However, to obtain the maximum output from a given oscillator, it is essential that both the phase and the amplitude of the energy fed back be correct.

A further object of the present invention is the provision of an improved oscillator circuit having' means for separately selecting the phase and the amplitude of the feed-back.

In most amplifier circuits, there is a tendency for energy to be fed back from the anode circuit to the grid circuit either through the interelectrode tube capacities or through the circuit externalto the tube. If, however, energy from the anode circuit, equal in amplitude to the aforementioned feed-back energy but opposite fin phase, is also fed back to the grid circuit,'it'will neutralize any tendency of the circuit to oscillate and provide greater stability of operation.

Still another object of the'present invention is the provision of an improved amplifier circuit having means for feeding back energy to'the grid circuit, which means, includes means for separately selecting the phase and amplitude of the energyfed back.

Amongst various forms of high frequency oscillator and amplifier circuits is the type referred to as the grounded grid type coaxialline arrangement in which the tube is arranged within a coaxial line and the grid substantially'isolates the anode-grid and-cathode-gridcircuits, except for the common ground line. V

A still further obj'ectof the present invention is the provision of an improved coaxial line oscillatorparticularly of the grounded-grid type.

Still another object of the present invention is the provision of an improved coaxial line amplifier, particularly ofthe grounded-grid type.

Other and further objects of the present invention will become apparent and the foregoing will be best understood from the following description of an embodiment thereof, reference being had to the drawing, in which the figure is a schematic diagram of one circuit embodying my invention.

The circuit illustrated in the figure may be used as either an amplifier or an oscillator as will be made clear'hereinafter. The circuit consists primarily of an outer metal cylinder l within which is mounted, in some suitable manner, an electron discharge device such as a vacuum tube triode 2, Tube '2 is preferably of the type having oppositely positioned anode and cathode elements 3 and 4 respectively, and a centrally positioned grid 5 having a generally radially-extending terminal'fi passing through the surrounding envelope 1 of the tub e.j The terminal 6 is preferably secured to and electrically connected with the inner surface of cylinder l in any suitable manner. Where terminal 6 isof insuiiicient diameter to properlyfit within cylinder i, an annular member of grea'terdiameter may be used to connect terminal 6 to the interior surface of outer cylinder 1 in a manner known in the art.

Outer cylinder I serves as the outer conductor of a, pair of coaxial lines generally designated by the numerals 8 and 8 extending on opposite sides of terminal 6; The inner conductor ID of coaxial line 8 is connected to the cathode 4 of tube 2 While the inner conductor ll of coaxial line 9 is connected to the anode 3 of tube 2. It will thus be seen that terminalt and grid 5 serve ,to substantially isolate theanode-grid and cathode-grid circuits from each other. Coaxial lines 8 and 9 may be tuned by anysuitable means such as, for example, shorting plungers I2 and 53 respectively.

In-the arrangement thus far described, there is relatively little feedj-back-from the anode-grid circuit to the cathode-grid circuit, the former of which may be considered as the output circuit and the latter, as the input circuit. In accordance with my invention, I provide means for feeding back energy from the anode-grid circuit to the cathodegrid circuit and this means includes means for controlling the phase of energy fed back and separate means for controlling the amplitude of said energy. e e

The feed-back circuit, generally designated by thenumeral' I4, is preferably comprised of three transmission lines, which for the sake of clarity will be referred to hereinafter as the phase line it, amplitude or stub line It, and connecting line ll;

Phase line I5, from which the phase of the feedback is selected, may be an unbalanced line, such as the coaxial line illustrated, dr a balanced line, and is of a length preferably electrically equally to or greater than one wavelength at the maximum Wavelength at which the circuit of the figure is designed to operate: Energy from axial linB is fed to phase line l5. by ailyj'suitable means. As illustrated in the figure, one way of doing this is by coupling the inner conductor I8 of phase line to the inner conductor I| of coaxial line 9 by means of a probe -"which is' preferably capacitively coupled to said inner c 9n..;; ductor H, the outer conductor ll' of phaseline; l5 being connected to the outer cylinderzllgw In order that maximum energy may be transferred from the anode-grid circuit to "phase line Iil connecting line I! is so coupled to line l6 that the point of such coupling may be varied. One way of accomplishing the foregoing is, as illustrated, by coupling the inner conductor 26 of connecting line I! by means of a probe 21 to the inner conductor 23 of line I6 while the outer V, conductore zti pf ,line I1, is connectedrto the outer conductor-22ofline l6; Outer conductor 22 is preferably longitudinally slotted as is known in the art to permit the probe to be moved back and forth alonginner conductor 23.

Th'ebonnecting line I 1 then delivers the energy Y V.which,has been-selected in phase by moving probejd-"andselected in amplitude by moving probe ,21, ,tothecathode-grid circuit. For this purpose the outerconductor 28 of line I! is conl5, the point at which probe 20 is coupledyto ole. or in part of the ,load' to which energy iromthe circuit shown in thefigureis supplied. i'irtfwinjheseen that along the length of line [5, the'phase ofthe energy travelling therealongwill Ivan and by selecting, the point.along line l5 hich ene'rgyis derived therefrom, any selected phasemay be obtained. v lworeover, since phase, line ,l5 is. preferably greater than one I the lineso that" no standing waves 5 uced. The impedance 2| may consist wavelengthit will be seen thatany phaseangle fi'jon'iifzeroto 360 .can thus be obtained. For-the purpose of selecting the amplitude, amplitude linellfi rnay be. connected to phaselinelS in the g'mannern The outer conductor 22,,of

$ 2 duc'tor 2'3 of"lin'e l. 6.is connected to the inner conductor [8 of line [5 by any suitable .means, asjprobe 24, so that the. probe 2 4 rnay be niene along inner conductor;l8 and coupled to a lected point thereon. To, permit moving 6 r tlitudehne- 'lfi'along l haseline [5 in t ey abovefd'escribed manner, the outer conductorls art. v

gur is adapted to be operatedat variou's wavelengths by adjusting plungers IZ and ;.l 3 of co,

a al',.line s 8.and.9, means are also preierably dedg for tuning resonant line l6 so that it is a uarter wavelength at the selectedirequencm.

S h means may consist of a plunger adapted to the effective length oij'line l6. l fns will be apparent tothose versed in theart, the'amplitude of the potential along the quarter wavelength line varies progressively'from -a maximum at the open end of said lineto a minimum at the shorted end'of said line. It will,

thereforebe apparent that by selecting various pointsalong the line, avoltage of a desired amplitude may be obtained. For this purpose, the.

de line; lfiis connected tofthe outer con- 9, of phaseline 15 While the innercon of, phase line 'IE may be slotted as is known in,

Amplitude line it item which is selected the if the impedance 2| *nectedto-outei*metal cylinder I while inner conductpr 2;6. 'of line I! is coupled to inner conductor ID of line 8 by a probee29. Probe 29 is adapted to be moved along the inner conductor l0 tov select the precise point e1; which the e'ne'r'gy,fe eel-bad; matt ;.Q deg 'e s" s p d; t us enabling the selection of an optimuni pointlfor the teed-back of energy.

rection? I t;jwi1 1 1 e seen that theadjustin g probe ZTaIonginne nductor zaen ieesi'ned mph tude offeed back may be obtained and th u s the lenergy derived from the anodekgrid vcircuit may be. appdrtionedfto the impedance ll and the cathode grid circuit; Ih e 'applicati0n of the various direct curren t potentials -is not hereshown since it is wellknown to those versed in the are. Other details r mingj part of this invention are ;also d 'is'ince they are likewise known in the, For example, whe the circuit illustrated the figure is used as anamplifler, various own means may be us ed: to apply the in coming signal to the cathode-grid circuit, F ne: th i ei Will e ze tha the dack; circuit must not galvanic ally connect theanode. and 'athode, and that some form of blocking con-.-

rangement should be employed in said:

circui. t a j -,It1 will be seen that I have provided a'circuit in which thefeedbackis separately controlled.

1 While I haveIderib ed the. details of one circuit-embodying my; invention, it .will be apparent that numerous. modifications may be made without departing froimthe teachings thereof. For example, while: I have stated that the impedance2-lrshould pref-a erably match the surge-"impedance of the line so that no standing waves are-produced, thereby obtaining ,awgradual and smooth transition in phase along line [5, it will'be obvious that even does not match the lineand standing waves exist on.the.,-line there-will nevertheless be obtained a-phase transition alongsaid line: enablingthe selection of any desired phas'e.

; Qbviously nvarious. formsi of coupling along a l transmission-line other than the probe arrangefeed-back circuit may be reversed in its connections to the anode-cathode'circuit such as, for example, by coupling phase line l5- to coaxial line 8 and coupling line I! to coaxial line 9. Various additional tuning arrangements other than the plungers shown likewise may be substituted, and other electron discharge devices other than the grounded-grid-triode may be used.

- While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objects of my invention and the accompanying claims.

I claim:

1. In an electron discharge arrangement having an input circuit and an output circuit, means for feeding back energy to the input circuit from the output circuit comprising a first transmission line coupled to one of said circuits, means for effectively terminating said first line to suppress standing waves along said first line, said first transmission line having an electrical length equal to at least one wavelength at the operating frequency of said arrangement, a second transmission line having an electrical length equal to a quarter wavelength at said operating frequency for establishing standing Waves along said second line, means for coupling said second transmission line to said first transmission line at selected intermediate points on said first transmission line, and means for coupling the other of said circuits to said second transmission line at .Selected intermediate points on said second transmission line.

2. In an electron discharge arrangement having an input circuit and an output circuit, means for feeding back energy to the input circuit from the output circuit comprising a first transmission line coupled to one of said circuits, said first transmission line having an electrical length equal to at least one wavelength at the operating frequency of said arrangement, a matching impedance terminating said line for suppressing standing waves along said line, a second transmission line having an electrical length equal to a quarter wavelength at said operating frequency for establishing standing waves along said second line, means for coupling said second transmission line to said first transmission line at selected intermediate points on said first transmission line, and means for coupling the other of said circuits to said second transmission line at selected intermediate points on said second transmission line. I

- 3. In an electron discharge arrangement having an input circuit and an output circuit, means for feeding back energy to the input circuit from the output circuit, said means including means for selecting the phase of the energy fed back substantially independently of amplitude, said phase selecting means comprising a transmission line coupled to one of said circuits, said transmission line having an electrical length equal to at least one wavelength at the operating frequency of said arrangement, a matching impedance terminating said line for suppressing standing waves along said line and means for coupling the other of said circuits to said line at selected points along the line, said last named means comprising a resonant transmission line section for producing standing waves along said resonant section.

4. In an electron discharge arrangement of the grounded grid coaxial line type wherein the electron discharge device is mounted within an outer conductive cylinder to which. thegrid is coupled and the anode and cathode of said device are coupled to separate inner -coaxial conductors, each of said inner conductors forming a separate coaxial line with the outer cylinder; means for feeding energy from'zone of said coaxial lines to the other of said coaxial Iines,:said means comprising a non-resonant transmission line, means for effectively terminating said line to suppress standing waves along said line, means for coupling said line to selected points on one of said coaxial lines, a resonant line coupled to said non-resonant line at variably chosen points on said non-resonant line to produce standing waves along said resonant line, and means for coupling said resonant line to selected points on the other coaxial line from variably chosen tapping points on said resonant line.

5. In an electron discharge arrangement having an input circuit and an output circuit, meansfor feeding back energy to the input circuit from. the output circuit comprising means for selecting the amplitude of the energy fed back, and separate means for selecting the phase of said fed back energy comprising a, fixed length of transmission line coupled to one of said circuits, a matching impedance terminating said line for suppressing standing waves along said line, and resonant transmission line means coupling the other of said circuits to selected intermediate points along said line.

6. In an electron discharge arrangement having an input circuit and an output circuit, means for feeding back energy to the input circuit from the output circuit at a given operating frequency comprising means for selecting the amplitude of the energy fed back, and separate means for selecting the phase of said fed back energy comprising a substantially fixed length of transmission line at said frequency coupled to one of said circuits, said transmission line having an electrical length at least equal to one wavelength at the operating frequency of said arrangement, a matching impedance terminatin said line for suppressin standing waves along said line at said frequency, and means coupling the other of said circuits to selected intermediate points along said line, said last named means comprises a section of transmission line having a fixed length at said operating frequency whereby standing waves at said frequency are produced along the length of said section.

'7. In an electron discharge arrangement having an input circuit and an output circuit, means for feeding back energy to the input circuit from the ouput circuit at a given operating frequency comprising a transmission line coupled to one of said circuits, means for terminating said transmission line in its characteristic impedance for suppressing standing waves along said line, and means for coupling the other of said circuits to variably chosen tapping points on said transmission line whereby the phase of energy fed back is controlled independently of its amplitude, said last named means comprises a section of transmission line having a fixed length at said operating frequency whereby standing waves at said frequency are produced along the length of said section.

ARMIG G. KANDOIAN.

(References on following page) .REEERENQES; CITED 'Thfoilowing references are of'record i'ri the filepf this patent: q

Number 4 Name 1 Date 2,107,387 Potter Feb. 8, 1938 2,284,405 McArthur- May 26, 1942 2,284,751 Linder June 2, 1942 2,362,209 Litton Nov. 7, 1944 10 Number Name Date DeRosa, Nov. 14, 1944 Segerstrom Jan. 23, 1945 Dow et a1 April 10,1945 Hansen et a1 May 8, 1945 Smith 1 July 9, 1946 DeRosa July 1, 1947 Doherty Aug. 26, 1947 Haefi April 20, 1948 

